This invention relates generally to gas turbine engines and more particularly, to butterfly valve assemblies used to regulate fluid flow to a gas turbine engine.
Gas turbine engines typically include an engine casing that extends circumferentially around a compressor, and a turbine including a rotor assembly and a stator assembly. The rotor assembly includes at least one row of rotating blades that extend radially outward from a blade root to a blade tip. A circumferential tip clearance is defined between the rotating blade tips and the engine casing.
During engine operation, heat generated by the engine may cause thermal expansion of the stator assemblies, and render the tip clearance non-uniform circumferentially. As a result, inadvertent rubbing between the rotor blade tips and the engine casing may occur. Continued rubbing between the rotor blade tips and engine casing may lead to premature failure of the rotor blade or loss of engine performance.
To facilitate optimizing engine performance and to minimize inadvertent rubbing between the rotor blade tips and the engine casing, at least some known engines include a clearance control system. The clearance control system supplies cooling air to the engine casing to control thermal growth of the engine casing to facilitate minimizing inadvertent blade tip rubbing. Because the engine casing should be thermally cooled circumferentially, the clearance control systems include a plurality of complex duct work and associated valves coupled circumferentially around the engine.
To facilitate controlling the airflow supplied through the duct work, at least some known clearance control systems include butterfly valves. Each valve assembly includes a valve body, a valve shaft, and a valve disk. The valve body is coupled to the ductwork, and the valve shaft extends through an opening in the disk to pivotally couple the valve disk to the body for controlling the fluid flow. To enable the valve disk to seat circumferentially against the valve body to stop fluid flow through the valve body, the shaft extends obliquely through the valve disk. More specifically, the disk is substantially flat and includes raised areas that extend outwardly from the flat portions of the disk to define a portion of the shaft opening.
During engine operation, the transition from the substantially flat areas of the disk to the raised areas creates an abrupt inlet contraction and an abrupt exit expansion that may facilitate increasing loss coefficients associated with the fluid flowing through the valve. The increased loss coefficients facilitate reducing the pressure of the fluid flowing through the valve. As a result, fluid is discharged from the butterfly valve at a reduced pressure in comparison to the pressure of the fluid entering the valve. The raised areas also reduce an effective flow area through the butterfly valve. Such pressure losses may reduce the effectiveness of the clearance control system.
In one aspect, a butterfly valve is provided. The butterfly valve includes a valve shaft and a valve disk. The valve disk has a centerline axis that extends through the valve disk. The valve disk also includes a shaft opening, an outer periphery, an outer surface, a first side, and a second side. The first side is opposite the second side. The shaft opening extends through the valve disk adjacent the centerline axis, and is sized to receive the valve shaft therein. The disk outer surface extends over the first and second sides, and is tapered between the outer periphery and the centerline axis over at least one of the disk first and second sides.
In another aspect, a method for operating a gas turbine engine is provided. The method includes directing airflow into an air supply pipe through a butterfly valve assembly that includes a valve disk that has opposed sides, an outer periphery, and an outer surface that extends over both sides and is tapered from the disk outer periphery to a centerline axis that extends through the valve disk, and channeling the air flowing through the air supply pipe to an engine clearance control system.
In a further aspect, a gas turbine engine clearance control system is provided. The clearance control system includes an air supply pipe and a butterfly valve that is configured to regulate an amount of airflow entering the air supply pipe. The butterfly valve includes a valve shaft and a valve disk. The valve disk has a centerline axis that extends through the valve disk. The valve disk includes an opening extending therethrough, an outer periphery, an outer surface, and a pair of opposing sides. The opening extends along the valve disk centerline axis, and the shaft extends through the opening. The outer surface extends over the disk sides and is tapered between the outer periphery and the centerline axis.